Sen. Tom Cotton (R-AR) is one of President Donald Trump’s closest allies in the Senate, advising Trump before the alleged “shithole” comments about Haitians and African immigrants and on the White House’s Iran policy. Cotton is also reportedly a frontrunner for the job of CIA director if current director Mike Pompeo replaces Secretary of State Rex Tillerson.

Cotton is a protégé of neoconservative pundit and Iraq war proponent Bill Kristol, who is now an avowed anti-Trump conservative, a tension that has had little visible impact on Cotton’s ability to position himself as an ally of the White House. But the quiet appointment of Bill Kristol’s son, Joseph Kristol, as Cotton’s legislative director in June, certainly raises questions about the close relationship between one of the Senate’s most outspoken Iran hawks and Bill Kristol.

Joseph Kristol’s resume shows little that would explain his sudden appointment in Cotton’s office. According to LinkedIn, he was “Engagement Manager” at Mckinsey & Company for three-and-a-half years, before which he served in the Marines for four years. (His LinkedIn bio closely matches a 2014 wedding announcement, leaving little doubt that he is Bill Kristol’s son.)

It’s curious that Cotton, who has sought a role in the Trump administration dating back to at least May 2016, when he pushed his name for consideration at a possible vice-president pick, would choose the son of one Washington’s most outspoken anti-Trump conservatives as his legislative director.

Cotton and Kristol’s relationship goes back to when Cotton was still in the Army and stationed near Washington. “Kristol saw a kindred spirt in Cotton’s aggressive national-security hawkishness and the men developed what Kristol describes as a ‘bond beyond pure policy,’” according to a 2014 profile of Cotton in The Atlantic.

That spending couldn’t legally be coordinated with Cotton’s campaign. But that doesn’t mean that the first-year senator couldn’t pay back his mentor and dark-money supporter in June 2017 by giving his son, Joe, a prime job in his Senate office.

Moreover, despite Bill Kristol’s family ties to Cotton’s Senate office, the elder Kristol and Cotton differ not only on their willingness to embrace to Trump but on key issues such as immigration.

Las week, Bill Kristol tweeted, “If you care about American Greatness, you should be for reasonably liberal immigration policies.” Two weeks ago, Cotton’s office, under the legislative guidance of Kristol’s son, signed on to a statement hitting on the same anti-immigration policy favored by the White House and ethnic nationalists like Stephen Miller. The statement read:

There has been no deal reached yet on the future of DACA in the Senate. Some of our colleagues have floated a potential plan that, simply put, isn’t serious. It is disingenuous to discuss providing status to, potentially, millions of individuals without taking credible steps to truly protect our borders and secure the interior.

It simply isn’t credible to consider any ‘deals’ that don’t make it easier to apprehend, detain and deport dangerous criminal aliens. We owe the American people better. Any deal that does not address the four pillars we have reiterated- ending chain migration, eliminating the outdated visa lottery, increasing border security, and solving the DACA situation – is no deal at all.

Indeed, Cotton and Kristol’s son may have tapped into the populism that Trump harnessed for his longshot bid for the White House.

Cotton and Joseph Kristol share similar bios—Harvard followed by military service. Their political careers also overlap by linking neoconservative foreign policy—extreme hawkishness toward Iran and kneejerk support of Israeli Prime Minister Benjamin Netanyahu’s Likud Party—with a program of social conservatism and nationalism that Bill Kristol and the older generation of neoconservatives typically reject. This combination of neoconservatism and populism establishes a potentially new kind of litmus test for Republicans in the age of Trump.

One thing is clear. Bill Kristol hasn’t publicly criticized Cotton or the legislative efforts undertaken by Joseph Kristol, even while Cotton emerges as one of the White House’s closest allies in the Senate and Bill Kristol continues to beat the drum as one of the holdout “never Trump” Republicans. Perhaps this is because his son and Cotton are holding strong on the issues of the biggest concern to Bill Kristol—and whoever put up the $1 million Kristol channeled to help Cotton win his Senate seat—even while abandoning the more socially liberal positions Kristol claims to uphold.